Geophones are seismic detectors that are spaced out at various points on the ground to sense upcoming reflections of acoustic waves that are produced by a seismic source. The geophones are electrically connected to a leader cable which goes to a recorder that produces traces which are representative of the outputs of the phones. The recording can be used to make stratigraphic maps that show the various layers in the earth where there is a substantial impedance mismatch, and such maps are highly useful in prospecting for underground oil and/or gas deposits.
A geophone typically has a spike on the bottom of its case which is pushed into the ground in order to locate the phone at a selected point. When the seismic operation is completed and the phones and leader cable are being gathered up for use elsewhere, it is not uncommon for personnel to go along the line and jerk the spikes of the phones out of the ground, using the leader cable to do so. The jerk force on the cable tends to break conductor wires and to disrupt electric connections, which will render a phone inoperable until repairs are made. Such repairs may not be easy to make in the field, in which case the phones or cable are out of operation until they can be returned to a shop for repairs.
Various proposals have been made for minimizing or eliminating this problem. For example, the Hall U.S. Pat. No. 3,931,453, the Sutherland U.S. Pat. No. 3,932,834 and the Woodall U.S. Pat. No. 4,438,292 each show the typing of a knot in the leader cable inside the top of the geophone housing where the cable enters to anchor the cable ends therein, so that jerking on it will be less likely to disturb the electrical connectors between the conductor wires and the geophone terminals. Of course, the knotting of an electrical cord inside the body of a male or a female electrical plug or socket has been a common practice. Although this approach has been widely used, it has the disadvantage that the small conductor wires in a leader cable are not good strength members, so that jerking forces can break them in tow in the region ahead of the knot. Moreover, a knot can become so tight that it is not easily undone, and the end portion of the leader cable containing the know will have to be cut off during repair. Generally speaking, if the leader cable itself is not a good strength member, then simply typing a knot in it as a stop against outward movement is not considered to be an optimum solution to the problem.
The general object of the present invention is to provide a new and improved leader cable and anchoring structure to a geophone which obviates the problems mentioned above.